The Pats have allowed 7.64 yards per rush since December started. As noted by NESN's Zack Cox, that three-week stretch of run defense is the worst in franchise history and among the worst recorded by any NFL team in the Super Bowl era.

And if there's a worse part for the Patriots, it's the fact they've surrendered these yards to teams that aren't particularly keen on running the ball.

Minnesota entered Week 15 as the league's second-worst rushing team by DVOA, yet nearly hit 100 yards on 13 carries on Dec. 2. Back in Werk 4, the Pats held the Dolphins to 56 rushing yards, then got blown to smithereens in Miami. And on Sunday, the Steelers trotted out their third and fourth-string backs, one of whom enjoyed his best rushing day since high school.

Pittsburgh compiled 158 rushing yards and barely broke a sweat.

So, what's to make of all this? New England coach Bill Belichick addressed the topic of his leaky run defense on a conference call Monday with reporters. He spoke generally on a range of topics from the source of problem, personnel decisions and game-planning.

"We always try to play with good fundamentals and technique, so that will never change. What we do schematically will depend on the game plan and what our opponent does and what we're trying to stop and so forth," Belichick said. "But fundamentally, we always try to play with good fundamentals and techniques."

Defensive tackle Danny Shelton, who tips the scales at 345 pounds, has been a healthy scratch this entire stretch. He's currently ranks as the league's No. 43 defensive tackle, by Pro Football Focus's player grades AKA perfectly average. So why has Belichick opted to sit him in favor of other players?

"It's not about any individual player," Belichick explained. "It's about each week we're allowed to activate 46 of our 53-man roster players to play, and so that's what we do. And we activate those players based on the particular opponent and game that we're playing."

Considering New England primarily played dime defense on Sunday -- deploying six defensive backs with a mix of five other linebackers and/or defensive linemen -- it was clear Sunday the Patriots wanted Pittsburgh to run. Perhaps the Steelers surprised them with their success, gaining 6.3 yards per handoff. But the final result nonetheless favored New England's defense: Pittsburgh was held to 17 total points, which tied for a season-low dating back to Sept. 30.

That number was largely a function of New England's effective pass defense that nabbed two interceptions and held arguably the league's top receiver duo to 89 total yards. And according to Belichick, the pass is what matters in today's NFL -- just like it always has.

"Well, I think the National Football League has always been a passing league, but the running game is very important," Belichick said. "Look, each week, you try to defend whatever the offense your opponents do -- running game and passing game, situational football, third down, red area and everything else.

"So what you do is a function of what they do, and that's really more of a week-to-week thing for us."